1. Field of the Invention
This invention relates to a scanning type copying machine. More particularly, this invention relates to a scanning type copying machine having an automatic image density control means and capable of copying a document such as a book by dividing the area of the document to be copied.
2. Description of the Prior Art
Copying machines having automatic image density control means are now put into practical use. As the prior art, Japanese Patent Laying-Open Gazette No. 2134/1979 discloses an automatic exposure control mechanism of a copying machine. According to this application, a density of a document is measured while a document table moves from an initial position to an exposure start position, so that the measured value is used for control of an exposure amount at the time of projecting an image of the document onto a photoreceptor. In addition, according to Japanese Patent Laying-Open Gazette No. 45564/1982, a density of a document is measured during transport of the document by an automatic document feeder and the measured value is used for control of the density for copy operation, namely, for development bias control. By using such automatic image density control means, a copy not fogged nor dimmed can be obtained automatically without error compared with a copy obtained by manually setting a density of a document.
On the other hand, irrespective of whether automatic image density control means is provided or not, copying machines having a dividing copy mode convenient for copying of a book or the like are known. One of such copying machines is disclosed in U.S. Pat. No. 4,017,173. The copying machine of this patent has a dividing copy mode and a normal copy mode. In the dividing copy mode of this patent, an opened book is placed on a document table and the respective opened pages are individually scanned by one copy start operation so that two copies are obtained. Such a copying machine having the dividing copy mode has advantages that such troublesome work as cutting of copies into halves is not required and binding of copies is easy compared with the case of copying a book in the normal copy mode.
Meanwhile, it may be proposed to apply the above described dividing copy mode to a copying machine comprising automatic image density control means. More specifically, a copying machine, according to such proposal, is adapted to detect an image density by preliminary scanning of the opened pages of a book regarded as one sheet and the optimum exposure amount is determined based on the detected image density so that two copies of appropriate density can be obtained by consecutive two scanning operations with the same exposure amount.
However, if the densities of the bases of the opened two pages are different, or if one of the two pages contains a region of a high density such as a photograph or a picture, it is pointed out that an exposure amount to be applied for such a copy operation is not suited to either of the opened pages.